FEMALE RED THROAT COLORATION IN TWO POPULATIONS OF THREESPINE STICKLEBACK

Abstract

Abstract In a population of stream-resident stickleback from British Columbia, females frequently have orange-red throats which are conspicuous to the human eye and, according to two straightforward physical measures of coloration, are more intensely red than the throats of anadromous females. Stream and anadromous males from these populations, however, do not differ for a reflectance-based index of red chroma. This suggests that exceptional female red coloration in the stream population has not evolved as a byproduct of the evolution of exceptional coloration in males. In contrast to results for female lateral barring in another threespine stickleback population, red is not strongly associated with reproductive readiness and unlikely to function strictly as a signal of readiness to mate. Larger stream females have more intensely red throats though this pattern was significant only in one year and according to one technique. With these findings and the extensive literature already available for this species, the threespine stickleback becomes a promising model system for studying the evolution of female secondary sexual characters in species with conventional sexual dimorphism.